A threaded nut or work piece is frequently locked to a threaded stud by applying a second nut or work piece in direct, face-to-face compressive relation against the first nut or work piece, to lock it in place. Traditionally, the two threaded members must be rotated (torqued) against each other in the fastening process, upon the threaded stud. The threaded stud is slightly stretched during this fastening process, in order to generate the required locking force between the locking nut and the work piece. In the case of large diameter threaded assemblies (e.g. 1″ diameter or larger) the torque required to produce the desired fastening effect become significant, and in some cases is impractical by standard hand tools. Instruments such as a load-meter, which are required to be locked in place, are unsuited to having such locking torque applied against them, and can be damaged by such torquing action.
In installations where the threaded stud is subjected to a large applied tensile load, the axial locking force at the locking interface must exceed the applied tensile load in order to ensure that the locked condition is maintained. This may require the application of excessive mutually opposed torquing force between the nut and the workpiece. Furthermore, some work pieces may be torque-sensitive and not suited or permitted to be tightened with such excessive torque, for example, such as an inline force transducer (load-meter) located in a load-applying tensile testing apparatus. However, a reliable locking mode is still desirable for these types of assembly.
An adjustable spacer, known as the “MTS 6011.11 Spiral Washers “has previously been used to provide a backlash-free threaded union. The MTS apparatus uses a pair of spirally tapered washers in facing relation, one of which is rotated about its polar axis relative to the other tapered washer, to change the extent of taper interplay, thereby increasing the axial extent of the washers, to take up the extension of a stud or other tensioned member. However, the Spiral Washers are NOT load jacking devices. Four major disadvantages of the MTS system are: (1) External tension force is needed to stretch the stud as the MTS Washers are not usable as a load-applying prime mover; (2) the requirement for special tools in order to rotate one washer relative to the other: (3) the MTS system may require the use of two hands; and (4) in order to access the washers and use the special tools in rotating the washer/washers a significant clear area adjacent the washers is required.